Note: Javascript is disabled or is not supported by your browser. For this reason, some items on this page will be unavailable. For more information about this message, please visit this page: About CDC.gov.

In 1993 we reported an association between exposure to radioactive iodine in fallout from nuclear weapons testing at the Nevada Test Site and the development of thyroid neoplasms in a cohort of 2473 exposed as children, and followed for up to 38 years. In 2001 when preparing to re-examine this cohort again we discovered errors in the dosimetry model used to assign individual radiation exposure, and corrected them. A panel of three medical experts, blinded to the exposure history of the subjects and using the most recent diagnostic criteria, reviewed the medical history of the 358 subjects with thyroid disease. Thirty were eliminated, and 18 others assigned a new diagnoses. Radioactive iodine exposure in the cohort ranged from 0 to 140 milliGray with a mean dose of 10.5 mGy. Using four levels of exposure the Rate Ratios for the highest exposure category compared to the lowest for all neoplasms changed from 3.4 (95% Confidence Interval 0.5-26.9) to 7.5 (95% CI 2.6-23.2, trend p = 0.00053), and 13.8 (95% CI 3.5-63.0) for benign neoplasms (trend p= 000112). Thyroiditis became significant with the RR changing from 1.1 to 2.9 (95% CI 1.7-5.2, trend p=O.00013). Exposure before age 8 to low doses of radioactive iodine was associated with increased risk of thyroid neoplasms and thyroiditis in this cohort. The findings agree with results from those exposed to radioactive iodine from the Chemobyl accident. This is the first report of increased risk of thyroiditis in this cohort, and among residents of the United States.